Methods of reducing chamber residues

ABSTRACT

The present disclosure relates to systems and methods for reducing the formation of hardware residue and minimizing secondary plasma formation during substrate processing in a process chamber. The process chamber may include a gas distribution member configured to flow a first gas into a process volume and generate a plasma therefrom. A second gas is supplied into a lower region of the process volume. Further, an exhaust port is disposed in the lower region to remove excess gases or by-products from the process volume during or after processing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/857,755, filed Apr. 24, 2020, which claims benefit of U.S.provisional patent application Ser. No. 62/848,337, filed May 15, 2019,each of which is herein incorporated by reference in its entirety.

BACKGROUND Field

Embodiments of the present disclosure generally relate to methods andapparatus for minimizing the formation of residues on chamber walls andhardware components during substrate deposition processes, such ashardware components of process chambers during deposition of thin filmson semiconductor substrates.

Description of the Related Art

Plasma-enhanced chemical vapor deposition (PECVD) can be used to formone or more thin films on a substrate for semiconductor devicefabrication. As semiconductor devices demand higher memory density dueto their continuously decreasing dimensions and the utilization ofmulti-stack structures, control of film properties of the semiconductordevices is of increasing concern. A major contributor of defects in thefilm formation process is the presence of residues in the depositionchamber, particularly residues deposited in undesired areas such as thechamber bottom and slit valve areas. The presence of such residues inthe chamber not only results in defective semiconductor devices, butalso increases cleaning time between deposition cycles, thus reducingoverall yield throughput and increasing manufacturing costs. Factorscontributing in the buildup of chamber residues include errantdispersion of plasma throughout the chamber and the formation ofundesired parasitic plasma.

Accordingly, what is needed in the art are improved methods andapparatus for minimizing the deposition and buildup of residues onchamber components.

SUMMARY

In one embodiment, a method for forming a film comprises introducing afirst gas into a process volume of a process chamber at a first flowrate, generating a plasma from the first gas to form a film on asubstrate disposed on a substrate support assembly, and introducing asecond gas into the process volume at a second flow rate. The second gasis introduced into a lower region of the process volume via a gasintroduction port disposed below the substrate support assembly. A ratioof the first flow rate to the second flow rate is between about 0.5 andabout 3.

In one embodiment, a method for forming a film comprises introducing afirst gas into a process volume of a process chamber at a first flowrate, generating a plasma from the first gas to form a film on asubstrate disposed on a substrate support assembly, and introducing asecond gas into the process volume at a second flow rate that accountsfor 40% of a total flow within the process chamber. The second gas isintroduced into a lower region of the process volume via a gasintroduction port disposed below the substrate support assembly.

In one embodiment, a method for forming a film comprises introducing afirst gas into a process volume of a process chamber at a first flowrate, generating a plasma from the first process gas to form a film on asubstrate disposed on a substrate support assembly, and introducingoxygen gas into the process volume at a second flow rate that accountsfor at least 40% of a total flow in the process chamber. A ratio of thefirst flow rate to the second flow rate is between about 0.5 and about3. The oxygen gas is introduced into a lower region of the processvolume via a gas introduction port disposed below the substrate supportassembly and facilitates a spontaneous combustion reaction to consumeunreacted species of the plasma below the substrate support assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, and may admit to other equally effective embodiments.

FIG. 1A illustrates a cross-sectional schematic view of an exemplaryprocess chamber according to one embodiment of the disclosure.

FIG. 1B illustrates a cross-sectional schematic view of an exemplaryprocess chamber according to one embodiment of the disclosure.

FIG. 2 illustrates a flow diagram of a method according to oneembodiment described herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

The present disclosure relates to systems and methods for reducing theformation of hardware residue and minimizing secondary plasma formationduring substrate processing in a process chamber. The process chambermay include a gas distribution member configured to flow a first gasinto a process volume and generate a plasma therefrom. A second gas issupplied into a lower region of the process volume to reduce errantdispersion of the plasma, reduce the presence of active radical speciesbelow the wafer plane, and actively clean the lower region. Further, anexhaust port is disposed in the lower region to remove excess gases orby-products from the process volume during or after processing.

FIG. 1A is a schematic cross-sectional view of a process chamber 100according to one embodiment. The process chamber 100 may be a plasmaenhanced chemical vapor deposition (PECVD) chamber suitable fordepositing a chemical vapor deposition film (CVD) film on a substrate,such as substrate 154. Examples of process chambers that may be adaptedto benefit as described herein include the PRODUCER® CVD processapparatus and PRECISION™ process apparatus commercially available fromApplied Materials, Inc., Santa Clara, Calif. Other suitably configuredprocess chambers, including those from other manufacturers or for otherapplications may also be used in accordance with the embodimentsdescribed herein. For example, embodiments described herein may be usedto benefit etch chambers, ion implantation chambers, and strippingchambers, among others.

The process chamber 100 may be used for various plasma processes,including deposition and removal processes. In one aspect, the processchamber 100 is used to perform CVD using one or more precursor gaseswith or without radio frequency (RF) power sources. In anotherembodiment, the process chamber 100 is used for PECVD processes.

The process chamber includes a chamber body 102 having sidewalls 106 anda chamber bottom 108 at least partially defining a process volume 120.The process chamber 100 further includes a lid assembly 110 and asubstrate support assembly 104. The substrate support assembly 104 isdisposed in the process volume 120 and is configured to support asubstrate 154 thereon during processing. The lid assembly 110 is coupledto the chamber body 102 at an upper end thereof, enclosing the substratesupport assembly 104 within the process volume 120. The substrate 154 istransferred to the process volume 120 through a slit valve opening 126formed in the sidewall 106. The slit valve opening 126 is selectivelyopened and closed to enable access to the process volume 120 by asubstrate transfer robot (not shown) for substrate transfer. In someembodiments, one or more process gases and cleaning gases may beintroduced into the process volume via the slit valve opening 126.

An electrode 109 is disposed adjacent to the chamber body 102 andseparates the chamber body 102 from other components of the lid assembly110. The electrode 109 may be part of the lid assembly 110, or may be aseparate sidewall electrode. An isolator 107, which may be formed of adielectric material such as a ceramic material or metal oxide material,for example aluminum oxide and/or aluminum nitride, contacts theelectrode 109 and separates the electrode 109 electrically and thermallyfrom other components of the lid assembly 110 and from the chamber body102. In one embodiment, the electrode 109 is sandwiched between opposingisolators 107 such that the isolators 107 are in contact with thesidewalls 106 and the lid assembly 110.

The lid assembly 110 includes a gas distribution member 112 having aplurality of openings 118 for flowing one or more process gases,precursors, or cleaning gases into the process volume 120. The gases aresupplied to the process chamber 100 from a first gas source 111 via aconduit 114, and the gases are flowed into a mixing plenum 116 prior toflowing into the process volume 120 via the openings 118. In oneexample, one or more inert gases may be flowed into the process volume120 during deposition or cleaning processes, such as argon, nitrogen,oxygen, helium, and the like. Other suitable examples of precursor gasesthat may be flowed into the process volume 120 during deposition includepropene, ammonia, tetraethyl orthosilicate, silane, and the like. Theone or more gases are introduced into the process volume 120 at a totalflow rate of between about 1000 standard cubic centimeters per minute(sccm) and about 20000 sccm, such as between about 5000 sccm and about15000 sccm, such as about 10000 sccm.

The gas distribution member 112 is further coupled to a power source142, such as a radio frequency (RF) power source, configured to providea power to the gas distribution member 112. In one embodiment, acontinuous or pulsed RF power is utilized to form a plasma in theprocess volume 120. In other embodiments, a continuous or pulsed DCpower is utilized to form a plasma in the process volume 120. The powersource 142 provides a power of between about 100 Watts and about 3000Watts at a frequency between about 50 kHz and about 13.6 MHz.

In operation, the process gases or precursors are supplied to theprocess volume 120 from the first gas source 111 and flow through theplurality of openings 118 in the gas distribution member 112. A plasmais formed in the process volume 120 by activation of the process gasesor precursors by RF power supplied by the power source 142 to the gasdistribution member 112. The plasma forms films on, or etches filmsfrom, the substrate 154 that is supported by the substrate supportassembly 104.

The substrate support assembly 104 is formed from a metallic or ceramicmaterial, such as a metal oxide material, a metal nitride material,metal oxynitride material, or any combination thereof. For example, thesubstrate support assembly 104 is formed of an aluminum-containingmaterial, an aluminum nitride-containing material, an aluminumoxide-containing material, or an aluminum oxynitride-containingmaterial. The substrate support assembly 104 includes a substratesupport surface 180 disposed on a first surface thereof, parallel to asecond surface of the substrate support assembly 104 and facing the lidassembly 110. The substrate support surface 180 is configured todirectly support the substrate 154 during processing. The substratesupport assembly 104 is coupled to a lift mechanism 147 through a shaft144, which extends through an opening 146 in the chamber bottom 108. Thelift mechanism 147 enables the substrate support surface 180 to be movedvertically through the process volume 120 between a lower transferposition and one or more raised process positions.

An electrostatic chuck (ESC) 130 is disposed in the substrate supportassembly 104. The electrostatic chuck 130 includes one or moreelectrodes 122. The electrodes may be a plate, a perforated plate, amesh, a wire screen, or any other distributed arrangement. The one ormore electrodes 122 are coupled to an electrode power source 124 toprovide power to the electrodes 122 and facilitate chucking of thesubstrate 154 to the substrate support surface 180 during processing ofthe substrate 154. In one embodiment, the electrode power source 124applies a DC voltage to the electrodes 122 for chucking. The electrodepower source 124 is capable of producing either or both of continuous orpulsed power.

In some embodiments which can be combined with other embodiments, thesubstrate support assembly 104 includes additional electrodes (notshown) for use in combination with the electrode 109 to generate plasmaduring the processing of the substrate 154. The use of the electrode 109and the additional electrodes disposed in either the substrate supportassembly 104 or proximate the substrate support assembly 104 to generateplasma may have a variety of embodiments. For example, an RF field maybe created by driving at least one of the electrode 109 and theadditional electrodes with drive signals to facilitate formation of acapacitive plasma within the process volume 120. In one embodiment, theadditional electrodes are used in combination with the electrode 109 tobias the plasma in the process volume 120. The electrode power source124 provides an RF power to the electrodes 122 or additional electrodesof up to about 1000 W at a frequency of about 13.56 MHz. However, it iscontemplated that other frequencies and powers may be provided dependingon the application. For example, the electrode power source 124 mayprovide multiple frequencies, such as 13.56 MHz and 2 MHz.

The substrate support assembly 104 further includes a heater apparatus140 disposed therein and coupled to a heater power source 148. Theheater apparatus 140 is used to heat the substrate 154 and mayincidentally heat the process volume 120 during the processing of thesubstrate 154. In one embodiment, the heater apparatus 140 is aresistive heater. In another embodiment, the heater apparatus 140 is achannel adapted to receive a flow of heated or cooled fluid, such asair, nitrogen, helium, water, glycol, or the like, therethrough toconduct heat to the substrate 154.

One or more gas introduction ports 162 are disposed through the chamberbody 102 below the substrate support assembly 104 and are coupled to asecond gas source 113. In one embodiment, the one or more gasintroduction ports 162 are formed through the sidewalls 106 adjacent toa lower region 150 of the process volume 120. In another embodiment, theone or more gas introduction ports 162 are formed through the chamberbottom 108 separate from the opening 146, as depicted in FIG. 1A. In yetanother embodiment, the opening 146 itself functions as a gasintroduction port that may be utilized alternatively to or incombination with the one or more gas introduction ports 162.

The second gas source 113 supplies one or more process gases,precursors, cleaning gases, or barrier gases into a lower region 150 ofthe process volume 120 through the gas introduction ports 162 and/oropening 146. Alternatively or additionally, one or more gases may besupplied into the lower region 150 via the slit valve opening 126. Thesecond gas source 113 controls the type of gas and the flow rate of thegas into the process volume 120, and more specifically, to the lowerregion 150. In one embodiment, the second gas source 113 supplies apurge gas into the lower region 150. The purge gas may be an inert gas.Additionally, the purge gas may be formed of a species having relativelylow reactivity (e.g., a non-reactive species) relative to the gasessupplied by the first gas source 111 and having a dissociation energygreater than that of diatomic argon. For example, the purge gas may beformed of a species having a dissociation energy greater than about 4.73kJ^(mol−1). For example, the purge gas may be formed of any one ofhelium, argon, oxygen, nitrogen, hydrogen, ammonia, or any combinationthereof. In such an example, ionization of the second gas in the lowerregion 150 is mitigated or prevented.

An exhaust port 152 is in fluid communication with the process volume120 and extends through the chamber body 102. In one embodiment, theexhaust port 152 is disposed through a sidewall 106. It is contemplatedthat the exhaust port 152 may be an annular pumping channel surroundingthe process volume 120, or a non-annular pumping port adjacent theprocess volume 120. In another embodiment, the exhaust port 152 isdisposed through the chamber bottom 108. The exhaust port 152 is coupledto a vacuum pump 156 to remove excess process gases or by-products fromthe process volume 120 during or after processing of the substrate 154.

In operation, process gases or purge gases are supplied to a lowerregion 150 below the substrate support assembly 104 from the second gassource 113 via the gas introduction ports 162, the opening 146, and/orthe slit valve opening 126. The process gases or purge gases aresupplied to the lower region 150 by the second gas source 113 while aplasma is formed above the substrate support assembly 104 to deposit oneor more films on the substrate 154. Thus, the first gas source 111 andthe second gas source 113 simultaneously supply gases to the processvolume 120, albeit from different regions of the process chamber 100.

In certain embodiments which can be combined with other embodiments, thegas species supplied by the second gas source 113 react with theactivated plasma species to form byproducts that are exhausted throughthe exhaust port 152. This may occur, for example, if the activatedplasma species diffuses into the lower region 150, or if the second gasdiffuses into an upper region of the process region 150. In certainembodiments, the gas species supplied by the second gas source 113 hasno (or minimal) reactivity with the activated plasma species, but ratherdilutes the activated plasma species in the process volume 120 (or inthe lower region 150) before being exhausted through the exhaust port152. In such an example, the dilution mitigates unwanted deposition inthe lower region 150.

FIG. 1 B is a schematic cross-sectional view of the process chamber 100according to another embodiment. The process chamber 100 depicted inFIG. 1 B is substantially similar to the embodiments described above butfurther includes a radiation shield 182 disposed below the substratesupport assembly 104. The radiation shield 182 is utilized to modulateradiation heat loss at a bottom surface of the substrate supportassembly 104 to compensate for any temperature non-uniformities of thesubstrate support assembly 104, and thus, a substrate 154 positionedthereon.

The radiation shield 182 includes a radiation shaft 184 and a radiationplate 186. The radiation shaft 184 is a tubular or cylindrical membersurrounding the shaft 144. A space 176 is formed between the radiationshaft 184 and the shaft 144 through which one or more gases suppliedfrom the second gas source 113 may be flowed. The radiation shaft 184further supports the radiation plate 186 and is formed of any suitablematerial for substrate processing, such as a quartz material.

The radiation plate 186 is a planar and disc-shaped plate that hassubstantially similar lateral dimensions to the substrate supportassembly 104. For example, the radiation plate 186 has a diameter thatis substantially similar to a diameter of the substrate support assembly104. The radiation plate includes a central hole through which the shaft144 extends. The radiation plate 186 may further include one or moreholes disposed radially outward of the shaft 144 to enable lift pins(not shown) to actuate therethrough. In one embodiment, the radiationplate 186 is formed of an aluminum oxide or aluminum nitride material.

In operation, the radiation shield 182 may direct one or more gasessupplied from the second gas source 113 through the space 176, along thebottom surface of the substrate support assembly 104, and towards thesidewalls 106. For example, the radiation shield 182 may control theflow of the one or more gases such that the gases flow radially outwardalong the bottom surface of the substrate support assembly 104 andtowards the sidewalls 106 in a flow path substantially parallel to thesubstrate support assembly 104. Thus, the radially outward flowing gasesmay form a gas curtain between the lower region 150 and the remainder ofthe process volume 120 that is substantially parallel to the substratesupport assembly 104. The radiation shield 182 may be used alternativelyto or in combination with the gas introduction ports 162 and/or the slitvalve opening 126 to introduce gases into the process volume 120, suchas the lower region 150.

As discussed herein, film deposition operations can include theformation of one or more films on the substrate 154 positioned on thesubstrate support assembly 104. FIG. 2 illustrates a flow chart of amethod 200 for processing a substrate, according to one or moreembodiments. The method 200 may be employed to form one or more films onthe substrate 154.

At operation 210, a plasma is generated in the process volume 120 of theprocess chamber 100. For example, a first gas is introduced from thefirst gas source 111 to the process volume 120 via the conduit 114. Thefirst gas is introduced into the process volume at a flow rate ofbetween about 1000 sccm and about 20000 sccm, such as between about 8000sccm and about 12000 sccm. The first gas includes at least a processgas, a precursor gas, an ionizable gas, or a carrier gas, which areactivated in the process volume 120 to form the plasma. For example, thepower source 142 provides an RF power, such as a continuous or pulsed RFpower, to the gas distribution member 112 to activate the first gas intoa plasma. Further, the first gas is utilized to form a film on thesubstrate 154 in the presence of the plasma.

At operation 220, a second gas is introduced into the lower region 150below the substrate support assembly 104 as plasma is generated abovethe substrate support assembly 104. For example, the second gas isintroduced into the lower region 150 from the second gas source 113through one or more gas introduction ports 162 formed in the sidewalls106 and/or the chamber bottom 108. In another example, the second gas isintroduced into the lower region 150 through the opening 146 between theshaft 144 and the chamber bottom 108. In yet another example, the secondgas is introduced into the lower region 150 through the space 176between the radiation shaft 184 and the shaft 144. The second gas is anon-reactive gas or a gas having a relatively low reactivity and may beformed of a species having a dissociation energy greater than that ofdiatomic argon. For example, the second gas is oxygen. Alternatively oradditionally, the second gas may be any one of hydrogen, helium, argon,or ammonia, among others.

The second gas may be simultaneously introduced into the process volume120 along with the first gas and function as a barrier curtain, reducingthe amount of errant dispersion of the plasma and unreacted speciesthroughout the process chamber 100, and particularly into the lowerregion 150. For example, the second gas, such as argon or nitrogen,functions as a dispersion trap, localizing the plasma and unreactedspecies above the substrate support assembly 104 and reducing diffusion(e.g., migration) elsewhere. The reduction of errant dispersion, inturn, reduces the formation of residues on chamber components, such asthose components in the lower region 150 (e.g., below the substratesupport assembly 104). In certain embodiments, the low reactivity of thesecond gas enables the second gas to function as trap withoutinteracting or mixing with the plasma. Furthermore, the low reactivityof the second gas facilitates the reduction of active plasma speciespresent in the lower region 150, thus reducing deposition of chamberresidues formed by parasitic plasma below the substrate support assembly104.

In another capacity, the second gas may function as a purge or cleaninggas, aiding in the removal of excess process gases or by-products fromthe process volume 120 during or after processing via the exhaust port152. For example, the second gas may facilitate spontaneous combustionof unreacted process gases that migrate below the substrate supportassembly 104. For example, in embodiments wherein oxygen is utilized asthe second gas, the oxygen gas may facilitate a spontaneous combustionreaction consuming unreacted hydrocarbons, such as C₃H₆, dispersed belowthe substrate support assembly 104, resulting in CO₂ and H₂O gases whichcan then be removed via the exhaust port 152. Thus, the second gas mayactively clean the lower region of the process volume 120 as films aresimultaneously deposited on the substrate 154 above.

In certain embodiments which can be combined with other embodiments, thesecond gas is provided to the lower processing region 150 to activelyinduce a reaction between the second gas and any of the first gas (e.g.,the activated species) in the lower processing region 150, whilesimultaneously providing a barrier for entry of the first gas into thelower region 150. The first gas and the second gas may react to form agaseous byproduct which is exhausted from the process chamber 100,mitigating or avoiding deposition of material in the lower region 150 ofthe process volume 120. In such an example, the second gas may be areactive gas (e.g., a gas which reacts with the excess precursormaterial). For example, the first gas process may be a hydrocarbon whilethe second gas is oxygen or ozone. In such an example, the reactionbetween the first gas and the second gas is a combustion reaction. Thecombustion reaction may occur in the lower processing region 150. In oneexample, the combustion reaction does not occur, or minimally occurs, inthe process volume 120 above the substrate 154.

The flow rate and type of second gas may be based on the flow rate ofthe first gas, the species of the first gas, the amount of plasma to begenerated, the characteristics of the deposited film, the amount offirst gas to be reacted with the second gas, and/or the amount of plasmadispersion to be prevented. For example, the second gas is flowed intothe process volume 120 such that the second gas accounts for greaterthan about 25% of the total gas flow in the process volume 120 to dilutethe first gas. For example, the second gas accounts for greater thanabout 30% of the total flow in the process volume 120, such as about 40%of the total flow. In certain embodiments, the flow rate of the secondgas is determined based on the concentration of the second gas speciesin the deposited film (e.g., nitrogen or oxygen). In some embodiments,the flow rate of the second gas is different than the flow rate of thefirst gas. For example, a ratio of the flow rate of the first gas to aflow rate of the second gas is between about 0.5 and about 3. Forexample, a ratio of the flow rate of the first gas to a flow rate of thesecond gas is between about 1 and about 2. In one embodiment, the secondgas is flowed into the process volume 120 at a flow rate between about50 standard cubic centimeters per minute and about 5000 sccm, such asbetween about 500 sccm and about 4000 sccm. For example, the second gasis flowed into the process volume 120 at a flow rate between about 1000sccm and about 3000 sccm, such as about 2000 sccm.

At operation 230, the plasma and the second gas are exhausted from theprocess chamber 100 through the exhaust port 152. For example, theexhaust port 152 may be coupled to the vacuum pump 156, and the vacuumpump 156 may remove excess process gases or by-products from the processvolume 120 during or after processing of the substrate 154.

Utilizing the systems and methods described above provides numerousimprovements in substrate processing operations. In particular, themethods described above provide a proactive approach to reducing oreliminating the undesired formation and buildup of residues on processchamber components by reducing the errant dispersion of plasma andactive plasma species below the substrate support. As such, theoccurrence of defects in films formed by plasma processes and thecleaning time between plasma processing operations is reduced, resultingin improved overall yield throughput and decreased manufacturing costs.Methods disclosed herein are particularly advantageous in the depositionof carbon or carbon-based hardmasks. Methods herein provide multipleadvantages for reducing unwanted deposition, including providing a gasbarrier for mitigating activated precursors species in the lower regionof the process chamber at the gas/activated species interface at thesubstrate support plane. Additionally, methods herein facilitateunwanted deposition by inducing combustion reactions. Moreover, methodsherein facilitate unwanted deposition by diluting reactive species inthe lower region of the process chamber.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. A method for forming a film, the methodcomprising: introducing a first gas into a process volume of a processchamber, the first gas introduced into the process volume through a lidassembly of the process chamber at a first flow rate, wherein theprocess volume comprises a substrate disposed on a substrate support;generating a plasma from the first gas to form a film on the substrate;and introducing a second gas into the process volume at a second flowrate, the second gas introduced into the process volume via a portseparate from the slit valve opening, the port disposed in a sidewall ofthe process chamber and below the substrate support, the second gasintroduced into the process volume simultaneously with the first gas,wherein a ratio of the first flow rate to the second flow rate isbetween about 0.5 and about
 3. 2. The method of claim 1, wherein thesecond gas is unreactive with the plasma.
 3. The method of claim 1,wherein the second gas is formed of a species having a dissociationenergy equal to or greater than that of diatomic argon.
 4. The method ofclaim 1, wherein the second gas is selected from the group consisting ofargon, ammonia, helium, hydrogen, nitrogen, and oxygen.
 5. The method ofclaim 1, wherein the second gas comprises a purge gas or cleaning gas.6. The method of claim 1, wherein the second gas forms a dispersion trapfor localizing the plasma to a region above the substrate support. 7.The method of claim 1, wherein the second gas reacts with the first gasin a lower region of the process volume to form a reaction byproduct,and the reaction byproduct is exhausted from the process chamber.
 8. Themethod of claim 7, wherein introducing the first gas into the processvolume and generating a plasma from the first gas causes dispersion ofunreacted precursor species below the substrate support, and wherein thesecond gas facilitates a spontaneous combustion reaction to consume theunreacted precursor species dispersed below the substrate support. 9.The method of claim 1, wherein a ratio of the first flow rate to thesecond flow rate is between about 1 and about
 2. 10. A method forforming a film, the method comprising: introducing a first gas into aprocess volume of a process chamber, the first gas introduced into anupper region of the process volume through a lid assembly of the processchamber at a first flow rate, wherein the process volume comprises asubstrate disposed on a substrate support; generating a plasma from thefirst gas to form a film on the substrate; and introducing a second gasinto the process volume at a second flow rate, the second gas introducedinto a lower region of the process volume via a space between thesubstrate support and a shield disposed below the substrate support, thesecond gas introduced into the process volume simultaneously with thefirst gas, wherein a ratio of the first flow rate to the second flowrate is between about 0.5 and about
 3. 11. The method of claim 10,wherein the second gas is unreactive with the plasma.
 12. The method ofclaim 10, wherein the second gas is formed of a species having adissociation energy equal to or greater than that of diatomic argon. 13.The method of claim 10, wherein the second gas is selected from thegroup consisting of argon, ammonia, helium, hydrogen, nitrogen, andoxygen.
 14. The method of claim 10, wherein the second gas comprises apurge gas or cleaning gas.
 15. The method of claim 10, wherein thesecond gas forms a dispersion trap for localizing the plasma to a regionabove the substrate support.
 16. The method of claim 10, wherein thesecond gas reacts with the first gas in the lower region of the processvolume to form a reaction byproduct, and the reaction byproduct isexhausted from the process chamber.
 17. The method of claim 16, whereinintroducing the first gas into the process volume and generating aplasma from the first gas causes dispersion of unreacted precursorspecies below the substrate support, and wherein the second gasfacilitates a spontaneous combustion reaction to consume the unreactedprecursor species dispersed below the substrate support.
 18. The methodof claim 1, wherein a ratio of the first flow rate to the second flowrate is between about 1 and about
 2. 19. A method for forming a film,the method comprising: transferring a substrate into a process volume ofa process chamber through a slit valve opening of the process chamber,the substrate transferred onto a substrate support; introducing a firstgas into an upper region of the process volume of the process chamberthrough a lid assembly of the process chamber at a first flow rate, thelid assembly comprising a gas distribution member having a plurality ofopenings; generating a plasma from the first gas to form a film on thesubstrate disposed on the substrate support; introducing second gas intothe process volume at a second flow rate, the second gas introduced intoa lower region of the process volume via an opening in a sidewall of theprocess chamber and from a space between the substrate support and ashield disposed below the substrate support, the second gas introducedinto the process volume simultaneously with the first process gas,wherein a ratio of the first flow rate to the second flow rate isbetween about 0.5 and about 3; and exhausting the process volume via apumping channel of the process chamber.
 20. The method of claim 19,wherein the second gas is selected from the group consisting of argon,ammonia, helium, hydrogen, nitrogen, and oxygen.